If you see a black screen, it’s because the ISS is in darkness, over the night side of Earth.

If you see a grey screen, it means that they are switching camera views or the feed from the ISS is temporarily not available.

Want to be notified when the ISS is overhead your location at night, so you can observe it tracking across the sky? Check out http://spotthestation.nasa.gov/ and give the astronauts the #ISSWave as they pass by.